RU2798456C1 - Nuclear power plant control method and controller - Google Patents

Abstract

FIELD: nuclear power plant.

SUBSTANCE: invention is related to a method for controlling a nuclear power plant containing a nuclear reactor (3) with pressurized water. In the method, one or more control rods (16) are moved into the reactor core for power control, an injection device (22, 23, 24, 26, 28, 30) for injecting boric acid and/or deionized water into the primary circuit (5) to control reactivity. The method provides for a waiting period during which the nuclear reactor (3) operates at partial power until it increases the power to a target power exceeding said partial power. For the end of said period, the xenon reactivity and/or xenon concentration is calculated based on the actual xenon concentration, the actual iodine concentration and the waiting period obtained. On the basis of the obtained data, the predetermined position of the control rods is calculated, wherein said one or more control rods are positioned during the waiting period. If the waiting period exceeds the first predetermined time to raise the xenon concentration to the maximum value, then the rods (16) are moved to compensate for the loss of reactivity.

EFFECT: possibility of adapting the method to the selected power grid control mode to determine the contribution of xenon to the expected power increase phase.

14 cl, 10 dwg

Description

The present invention relates to a method for controlling a nuclear power plant containing a pressurized water reactor.

In addition, the present invention relates to a controller for a nuclear power plant.

The electrical network is fed with electrical energy generated by several types of energy sources. In particular, renewable energy sources such as wind and solar power are highly unstable. Therefore, nuclear power plants also need to participate more and more in the regulation of the grid in order to stabilize the grid. Grid control is performed through several grid control modes, namely primary control providing an immediate change in power within a few seconds to maintain the grid frequency, secondary control or load sensing operation in which a request for additional or less power is remotely made, while change of electricity must be provided no later than 15 minutes. The tertiary control mode provides medium and long-term power variation.

At present, the use of nuclear power plants for various control modes is rather difficult. For example, a nuclear power plant operator estimates xenon reactivity based on previous experience.

EP 0 540 951 A1 discloses a method and apparatus for controlling a nuclear reactor to minimize boron concentration during load-tracking operation. Therefore, the focus is on controlling the axial power distribution and the corresponding axial xenon oscillation during load sensing operation, in conjunction with the goal of minimizing the injection of boric acid and deionized water.

DE 10 2017 205 553 A1 discloses a method for predicting the xenon concentration during the power-up period of a nuclear power plant in load-sensing operation.

EP 2 686 851 B1 discloses a method for operating a pressurized water reactor during load sensing operation.

EP 2 157 582 A1 discloses a method for predicting xenon fluctuations. For this, the axial power distribution of the reactor is determined in order to quickly suppress xenon oscillations.

In view of the foregoing, it is an object of the invention to provide an improved nuclear reactor control method that can operate with high reliability in many different network control modes.

In accordance with one aspect, a method is provided for controlling a nuclear power plant comprising a nuclear pressurized water reactor having a reactor core that generates power, a primary circuit connecting the reactor core to a steam generator, one or more control rods that can be moved into the core reactor for controlling the power of the reactor core, an injection device for injecting boric acid and/or deionized water into the primary circuit for controlling the reactivity of the reactor core, the method comprising:

determination of the actual power of a nuclear reactor,

automatic determination of the actual xenon concentration, the actual iodine concentration and/or the actual xenon reactivity,

obtaining a target power and a power gradient to increase the power until the target power is reached,

characterized in that

a waiting period and/or a remaining waiting period are obtained during which the nuclear reactor operates at partial power until it increases the power to a target power exceeding the partial power,

calculate for the end of the waiting period and/or the remaining waiting period the xenon reactivity and/or the xenon concentration based on the actual xenon concentration, the actual iodine concentration and the obtained waiting period,

xenon reactivity and/or xenon concentration are calculated for the end of the power increase period,

calculating a predetermined position of the control rod at the beginning of the power increase for one or more control rods based on the calculated xenon reactivity and/or xenon concentration at the end of the waiting period and at the end of the power increase period so that the power increase can be performed using the control rods,

one or more control rods are positioned during the waiting period based on the waiting period and the predetermined position of the control rods at the beginning of the increase in power so that one or more control rods reach the predetermined position of the control rod at the beginning of the increase in power at the end of the waiting period.

Additional embodiments of the invention may relate to one or more of the following features, which may be combined in any technically feasible combination:

- the calculation of the target position of the control rod at the beginning of the increase in power is additionally based on one or more reactivity values and/or reactivity factors of the nuclear reactor, in particular on one or more reactivity factors of one or more control rods, the reactivity factor of one or more L-rods, change in reactivity due to difference in mean coolant temperature (ACT) between actual power and target power, change in reactivity due to difference between actual power and target power, and/or contribution to reactivity of a subsequent flow of injected boric acid or deionized water in combination with a factor boric acid in the primary coolant;

- calculation of the target position of the control rods at the beginning of the increase in power is additionally based on the target position of the control rods at full power and/or the target position of the L-rods at full power;

- if the waiting period exceeds the first predetermined time, which allows raising the xenon concentration to the maximum value, then additionally: one or more control rods are removed from the reactor core to compensate for the loss of reactivity due to an increase in the xenon concentration, and before the end of the waiting period, one or more control rods into the reactor core to a predetermined position of the control rods at the beginning of the increase in power;

- if the control rods reach the upper control limit or the full load position when exiting the core, then some amount of deionized water is added to maintain the reactor at partial power to compensate for the loss of reactivity due to the increase in xenon concentration, in particular to ensure reactor power controllability ;

the method also includes: determining a time limit for moving one or more control rods to a predetermined control rod position at the start of the power increase based on the actual position of the control rod, the predetermined control rod position at the start of the power increase, and the actual concentration of boric acid in the primary coolant, so that move one or more control rods into the reactor core to a predetermined position of the control rod at the start of increasing power to a certain time limit by injecting deionized water into the primary circuit, and adding deionized water to the primary circuit;

- the time limit is also determined based on the minimum deionized water supply rate;

- when the waiting period is shorter than the second predetermined time, while the second predetermined time is greater than the first predetermined time, one or more control rods (16) are moved to the reactor core after the xenon concentration has reached its maximum during the waiting period, for compensation for the increase in reactivity due to the decrease in xenon concentration.

- when the waiting period is shorter than the second predetermined time, while the second predetermined time is greater than the first predetermined time, the method also comprises the following: if, during the movement into the reactor core, the control rods reach the predetermined position of the control rods at the beginning of the increase in power, then boron is added acid into the primary circuit and maintain the control rods in a predetermined position to start increasing power, including to ensure the residual reactivity of the shutdown reactor;

- when the waiting period exceeds the second predetermined time, while the second predetermined time exceeds the first predetermined time, the method also comprises the following: after reaching the maximum xenon concentration during the waiting period, boric acid is added to the primary circuit to compensate for the increase in reactivity due to the decrease xenon concentration, while, in particular, until the end of the waiting period, the control rods remain in the position of the upper limit of regulation or in the position of full power until one or more control rods (16) move into the reactor core to a predetermined position of the control rods at the beginning of the increase in power;

- the first preset time corresponds to the time 2 hours after the xenon maximum or the time after the xenon maximum corresponds to 30% of the waiting time to the xenon maximum;

- the first preset time is from 6 to 10 hours and/or the second preset time is from 20 to 60 hours; and/or

- calculate the total reactivity, including the reactivity of xenon at the end of the waiting period and at the end of the power increase period to increase the power to the target power to calculate the desired position of the control rod at the beginning of the power increase.

In accordance with another aspect, a controller is provided for a nuclear power plant comprising a nuclear pressurized water reactor, having a reactor core that generates power, a primary circuit connecting the reactor core to a steam generator, one or more control rods that can be moved into the core reactor to control the power of the reactor core, an injection device for injecting boric acid and/or deionized water into the primary circuit to control the reactivity of the reactor core, the controller being configured to:

determine the actual power of a nuclear reactor,

automatically determine the actual xenon concentration, the actual iodine concentration and/or the actual xenon reactivity,

obtain the target power and the power gradient for the power increase period until the target power is reached,

characterized in that the controller is additionally configured to:

obtain a sleep period and/or remaining sleep period during which the nuclear reactor operates at partial power until it increases power to a target power that exceeds partial power,

calculate for the end of the waiting period and/or the remaining waiting period the xenon reactivity and/or the xenon concentration based on the actual xenon concentration, the actual iodine concentration and the obtained waiting period,

calculate xenon reactivity and/or xenon concentration for the end of the power increase period,

calculate a predetermined position of the control rod at the beginning of the power increase for one or more control rods based on the calculated xenon reactivity and/or xenon concentration at the end of the waiting period and at the end of the power increase period so that the power increase can be performed using the control rods,

to position during the waiting period one or more control rods based on the waiting period and the desired position of the control rod at the beginning of the increase in power so that one or more control rods reach the specified position of the control rod at the beginning of the increase in power at the end of the waiting period.

In accordance with embodiments of the invention, the controller is configured to perform the method described in this document.

Additional advantages, features, aspects and details are apparent from the dependent claims, description and drawings.

So that the way in which the above features of the present invention can be understood in detail, the more specific description of the invention summarized above can be read with reference to the embodiments. However, it should be noted that the accompanying drawings illustrate only exemplary embodiments of this invention and, therefore, should not be construed as limiting its scope, as the invention may allow for other equally effective embodiments.

The accompanying drawings relate to embodiments of the invention and are described as follows:

in fig. 1 is a schematic flow diagram of a method according to an embodiment of the invention,

in fig. 2 graphically shows the dependence of xenon reactivity on the increase in reactor power,

in fig. 3 schematically shows the control of the xenon reactivity calculation during the standby period and the wake-up period,

in fig. 4 schematically shows the model for determining the actual values of the content of iodine and xenon,

in fig. 5 schematically shows a model for predicting the xenon concentration,

in fig. 6 shows a plot of xenon concentration and control rod or D-rod position, boric acid supply, deionized water supply, and reactor power versus time for a first latency period that is less than 8 hours, corresponding to xenon maximum, and position(s) D -bar stays essentially at the value that is needed for the subsequent increase in power compared to operation in the secondary mode.

In FIG. 7 shows a graph of xenon concentration and control or D-rod position, boric acid supply, deionized water supply, and reactor power versus time for a second standby period that ranges from 8 hours to about 30 hours with a minimum injection of boric acid and deionized water. using control rods to compensate for xenon.

In FIG. 8 shows a plot of xenon concentration and D-rod position, boric acid supply, deionized water supply, and reactor power versus time for a third sleep period that is greater than about 30 hours, with the control rod in the full power position for extended low power operating mode (ELPO) using xenon to extract D-rods and deionized water using an automatic reactivity balance to return them to the correct position to enter the operating mode at the end of the adjusted waiting time.

In FIG. 9 is a graph illustrating the xenon concentration prediction error based on xenon prediction correction over 200 calculation steps, and

In FIG. 10 is a visualization of reactivity control to increase the power of a nuclear reactor on a process computer system for a reactor operator.

In FIG. 1 is a schematic flow diagram of a method according to an embodiment of the invention for a pressurized water reactor. The nuclear reactor 3 includes a pressure vessel which includes fuel rods in the reactor core. The nuclear reactor 3, in particular the reactor pressure vessel, is connected to one or more primary coolant circuits 5 or primary circuits 5 in which the coolant is driven by a main coolant pump 7 . One or more primary circuits 5 carry, by means of a coolant, to one or more heat exchangers 9 the heat generated by nuclear fission of the nuclear fuel in the fuel rods. The pressure in these primary circuits 5 is so high that there is no evaporation of the water or coolant circulating in the primary circuit.

One or more heat exchangers or steam generators 9 generate steam, for example from water or a secondary coolant circulating in one or more secondary circuits. The steam is then transported through one or more secondary circuits 11 to one or more steam turbines where the steam obtained from the secondary coolant expands and creates rotation which is used by one or more electrical machines to generate electrical power. The secondary coolant condenses and is fed back to heat exchanger 9.

The nuclear reactor 3 includes a plurality of rods that are adapted to be inserted between the fuel rods to control the power generated by the nuclear reactor 3. For example, the nuclear reactor includes so-called L rods 14 and D rods 16. way to control the local power density in the reactor core or axial power distribution. The D-rods or control rods 16 are designed to control the absolute power of the reactor core. The control rods 16 absorb neutrons, and depending on the depth of their insertion, it is possible to control the power generation of a nuclear reactor, for example, by influencing the neutron flux inside the reactor. Therefore, the control rods 16 can rapidly change the power of the nuclear reactor 3. The control rods 16 are organized into sets (or groups) of control rods 16. For example, the nuclear reactor 3 may include a plurality of sets of control rods 16, each of which includes 3 to 8 control rods 16.

Movement of the control rods 16 or a set of D-rods is possible between the position of the L-rods, in particular the position of the free end of the L-rods 14, for example, when the free end of the control rods 16 corresponds to the free end of the L-rods 14, and the fully inserted end position or lower the end position of the control rods 16. The free end of the L-rods 14 and the control rods 16 corresponds to the lower end if the rods are inserted from above the nuclear reactor 3. In an embodiment of the invention, the fully inserted end position of the control rods 16 ends almost at the bottom of the core of the nuclear reactor 3. For example , the lower end position is about 300 cm of insertion of the control rods 16. The depth of insertion of the control rods 16 and L-rods 14 is determined based on the free end extending into the reactor core. In this example, it is considered that the control rods 16 and L-rods 14 are inserted into the nuclear reactor 3 from above. Other types of nuclear reactors may have control rods 16 and L-rods 14 that are inserted from below. The fully inserted end position is then the upper end position of the control rods 16.

For example, a typical PWR (Pressed Water Reactor) of German design with an electrical power of about 1500 MW has 4 movable sets (or groups) of control rods 16 with 4 control rods each to control the power of the reactor. Such a reactor may have a set of L-rods, consisting of about 45 L-rods.

To monitor and control the nuclear reactor 3, a plurality of detectors are provided for continuously determining the neutron flux density, and in accordance with an embodiment of the invention, the so-called SPND tube (self-powered neutron detector) 18 is provided with eight times six detectors.

How to control axial power distribution and corresponding xenon axial vibrations with L-rods, according to embodiments of the invention, is part of the standard reactor control 58 as it is used with "adaptive power distribution control" in a German PWR. This "adaptive power distribution control" triggers the "xenon axial two-point calculation" module (one point for the upper and another point for the lower half of the core; input given by SPND tubes 18). The dynamics of "adaptive power distribution control" is adapted in such a way that the necessary change in the position of the L-bar occurs in parallel with the change in load. Thus, this adaptive power distribution control essentially does not require the injection of boric acid and deionized water to compensate for the change in the position of the L-rod, which is used to control the axial power distribution PD at part load. In other words, the change in the position of the L-rods to control the axial power distribution, with respect to reactivity, is compensated by the effect of reactivity due to the change in reactor power.

According to embodiments of the invention, sets of control rods 16 can be inserted one after the other. Control rod sets or control rods 16 only slightly affect the axial power distribution. The power of the nuclear reactor and thus the movement of the control rods 16 is controlled depending on the measurement of the average coolant temperature - ACT.

In accordance with the present invention, the minimization of BODE injection (boric acid and/or deionized water injection) is produced and provided by total reactivity control, which is adapted to several control modes associated with the power supply network.

In addition, the nuclear reactor contains sensors 20 to determine the power of the nuclear reactor 3, for example, from the neutron flux.

In accordance with embodiments of the invention, the power of the nuclear reactor 3 is controlled by power controlled at the generator level. The control rods 16 and L-rods 14 are then moved to match the power of the nuclear reactor 3 with the power required by the generator. When adapting the power of the nuclear reactor 3 also changes the temperature of the primary coolant. Higher power results in higher primary coolant temperature. The temperature of the coolant also affects the reactivity of the nuclear reactor 3.

The long-term change in reactivity, in particular due to xenon and fuel consumption, is controlled by changing the concentration of boric acid and/or deionized water. This addition of one of these two fluids may also be referred to as BODE addition or injection in the present specification. Boric acid in primary circuit 5 acts as a neutron absorber. Thus, at a higher concentration of boric acid, power or reactivity decreases. To increase the reactivity, deionized water is added to the primary circuit 5 in order to reduce the concentration of boric acid and thereby increase the reactivity. There are separate pumps 22, 23 for supplying deionized water 24 and/or boric acid 26 to primary circuit 5. Pump 22 is for injecting deionized water 24 and pump 23 is for injecting boric acid 26 into primary circuit 5. The amount of deionized water 24 and /or boric acid 26 can be controlled by valves 28, 30 and/or pumps 22, 23. Pumps 22, 23 only operate when BODE injection is required.

The control of a nuclear reactor is complicated by the fact that the concentration of xenon-135 (hereinafter referred to as xenon or Xe) in the reactor core has a complex time dependence. Xenon acts as a neutron poison or neutron absorber. The xenon values change over the course of several hours. Xenon arises as a result of a chain of fission reactions of nuclear fuel and disappears when neutrons are absorbed and due to the decay of xenon. However, the generation and absorption of neutrons occur with a time delay, so that for the actual and future power of the nuclear reactor, it is necessary to take into account the actual, past and future values of xenon, in particular for optimal control of the position of the control rods 16 through the concentration of boric acid (by BODE injection). When a nuclear power plant operates for a long time at constant power, the xenon concentration reaches an equilibrium or steady state. Xenon reactivity is a linear function of xenon concentration.

In FIG. 2 shows two examples of a nuclear reactor running for a certain time at partial power.

In FIG. 2(a), the power P _R is initially 100% (ie the full power of the nuclear reactor) and then is reduced to 30% of the full power. Partial power, which is 30% of full power, is then maintained for about 2 hours before the power is increased at point A to 98% of full power. At partial power, the xenon concentration and hence the xenon reactivity increases. At point B, the nuclear reactor reaches its target power of 98% of full power. As can be seen, the reactivity of xenon during power up, i.e. between points A and B, decreases as xenon-135 burns out in the reactor, which begins to absorb more neutrons and decreases in reactivity shortly after point A. As can be seen from FIG. 2(a), the decrease in xenon reactivity between point A and point B due to xenon burn-up is about 100 pcm, which corresponds to a movement of about 20% of the length of the set of D-rods or control rods.

In FIG. 2(b) the power P _R is initially 100% (ie full power of the nuclear reactor) and then reduced to 30% of full power. Partial power, which is 30% of full power, is then maintained for about 6 hours before the power is increased at point A to 98% of full power. At point B, the nuclear reactor reaches its target power of 98% of full power. As can be seen, the reactivity of xenon during power up, i.e. between points A and B, decreases as xenon-135 burns out in the reactor, which begins to absorb more neutrons and decreases in reactivity shortly after point A. As can be seen from FIG. 2(b), the reduction in xenon reactivity between point A and point B due to xenon burn-in is about 500 pcm, which corresponds to a movement of about 100% of the D-rod set or control rods.

Thus, it can be seen that the xenon concentration, and hence the xenon-based reactivity, largely depends on the waiting period and the previous operation of the nuclear reactor 3.

A nuclear power plant can be operated in several modes of operation related to the needs of the electrical network.

Primary control provides immediate power for a few seconds to maintain the mains frequency, while additional power is provided between 0 and 15 minutes (typically within seconds) to stabilize the mains frequency. The primary control is derived from the mains frequency deviation from the standard frequency.

In the secondary control mode, the required power of the power plant is provided at the latest after 15 minutes. This is also referred to as load tracking work. In secondary control mode, the request for additional power is remotely supplied through the target generator power, which can be changed in steps. Additional electricity must be provided within 15 minutes at the latest. Only the maximum power gradient dPG/dt and the power range are known in advance. The operating time at partial power can be several hours. Power changes are requested in a stochastic manner. In the secondary control, the target power P _R must be reached at any time, so that the control rods 16 must have a specific predetermined or predetermined position.

Tertiary control mode provides medium and long term power variation. In tertiary control, the duration and required power are determined between the grid operator and the reactor operator.

Primary control can be used in parallel with secondary and tertiary controls.

In tertiary control, the increase in power will be carried out after a waiting time in accordance with the agreement between the reactor operator and the grid operator. The power increase depends on the actual reactor power P _R , the target power P _R and the power increase, also called the power gradient dPG/dt. As stated above, the power request is provided by controlling the generator for the nuclear reactor. Thus, the power gradient dPG/dt that must be provided to the mains is also provided by the generator control. In tertiary control mode, this corresponds to the value used, and in secondary control mode, this corresponds to the maximum power gradient.

In FIG. 1, the block diagram includes several input values, in particular the actual reactor power P _R , which is measured by the sensors 20, the target power P _R 32, which, for example, is provided by the reactor operator, the waiting period 34, for example, is provided by the reactor operator, until the power is increased to the target power P _R 32, secondary network control 36, which can be activated or deactivated, for example, by button 36, primary network control 38, which can be, for example, activated or deactivated by button 38, reactivity factors 40, which are determined automatically, and a control setpoint impact predictor 42 for activating or deactivating control rod setpoint adjustment based on the overall reactivity balance.

The actual power P _R of the reactor can be determined in other ways, for example, by determining the power of the electric generator.

The reactivity coefficients 40 are obtained through a core design calculation that is performed for each fuel cell cycle. These coefficients are variables in the reactor control software and depend on the equilibrium concentration of boron in the reactor core, which decreases during the entire cycle of the fuel cell to compensate for fuel burnup. In other words, the reactivity coefficients are calculated based on the equilibrium concentration of boron in the reactor core. These variables are set through the service block when replacing fuel elements, respectively, during a planned shutdown of the reactor. In other words, a characteristic curve is used to determine each reactivity coefficient based on the equilibrium boron concentration of the nuclear reactor 3. The reactivity coefficients 40 change slowly during a fuel cell cycle. The equilibrium concentration of boron in the reactor core is the concentration of boric acid used when the nuclear reactor 3 is operated at a steady or constant power for a long period of time, in particular when the xenon concentration reaches a steady state value at full power. The set of reactivity coefficients used are explained below with the help of FIG. 10. Since the reactivity coefficients 40 change very slowly, they can be considered constant for calculating the reactivity balance. In other words, the reactivity coefficients are variables that depend on "full load days" in the actual fuel cell cycle (e.g. 1 year) or a related parameter (as a reference boron concentration at full load equilibrium conditions) and can be given as a characteristic through the interface or service reactor control module when replacing fuel elements in accordance with the design of the next core.

The block diagram in FIG. 1 includes an actual value calculation module 44 in which the actual xenon and iodine concentration values in the nuclear reactor 3, in particular in the core of the nuclear reactor 3, are calculated based on the actual and past power P _R of the nuclear reactor 3. The actual xenon value is also indicated in Fig. 1 as Xe-value, and the actual iodine value is designated as J-value. In other embodiments, as shown in FIG. 4, xenon reactivity ρ _Xe is provided instead of xenon concentration.

In FIG. 4 shows the calculation of the actual xenon and iodine concentrations based on the actual and past power P _R of the nuclear reactor. The calculation is adapted to the type of nuclear reactor 3 and nuclear fuel loading. The input value is the actual power P _R of the nuclear reactor. Cells with designations Г _Xe , λ _J , λ _Xe , BXE, A _J , AXE are linear functions with known parameters. Cells with a cross are multipliers. The past power values P _R of the nuclear reactor 3 are taken into account by the integrator 45a, taking into account the concentration of iodine. In other words, the integrator obtains the actual iodine concentration by integrating the difference between iodine production and iodine breakdown. The decay of xenon and the loss of xenon due to neutron absorption are subtracted from the sum of xenon directly produced and xenon from iodine decay. The integrator 45b calculates the actual xenon concentration value from the xenon concentration gradient. In the embodiment shown in FIG. 4, when calculated using G _Xe, the actual xenon reactivity ρ _Xe is obtained. For example, the value of xenon reactivity is indicated in units of pcm - millionths of a percent.

The block diagram in FIG. 1 also includes a prediction module 46 . The prediction module performs cyclic prediction of the concentration of xenon, and in particular iodine, in the nuclear reactor 3, in particular in the core of the nuclear reactor 3.

The prediction module 46 predicts the xenon concentration for the sleep period, in particular for the end of the remaining sleep period and the end of the power increase period. For this, the prediction module receives the actual xenon and iodine concentration values from the actual value calculation module 44, the time Δt _{ramp up} required to increase the power, and the reactor power setpoints P _R for the waiting period and the power increase period from the control module 48.

The control module 48 outputs all the necessary values for predicting xenon based on the input value of the target power P _R , based on whether the nuclear reactor 3 should operate in the secondary control mode (obtained from the module 36), the remaining waiting period and the actual power P _R of the nuclear reactor 3.

The operation of the prediction unit 46 will be explained with respect to FIG. 3 and 5. The prediction module 46 iteratively calculates the xenon concentration and thus the xenon reactivity. In an embodiment of the invention, the iodine concentration values are also calculated. Cells with designations Г _Xe , λ _J , λ _Xe , BXE, A _J , AXE are linear functions with known parameters. Cells with a cross are multipliers. An integrator 48a is used to take into account the dependence of the iodine concentration on time. In other words, the integrator obtains the iodine concentration value by integrating the difference between iodine production and iodine breakdown. Xenon decay and xenon losses due to neutron absorption are subtracted from the sum of xenon directly produced and xenon from iodine decay. The integrator 48b calculates the actual xenon reactivity concentration ρ _Xe from the xenon concentration gradient dXe/dt. To start prediction, the xenon concentration actual value and the iodine concentration actual value are read once at the beginning of the prediction operation. Module 48c starts each step of the calculation with a certain increment of time, as will be explained below. Using G _Xe in the calculation, predicted values of xenon reactivity ρ _Xe for the end of the waiting period or the end of the power increase are obtained, as will also be explained below. According to embodiments of the invention, the end of the sleep period corresponds to the start of the power ramp.

The (remaining) waiting period and the power increase period are divided into a predetermined number of steps for calculation. According to the example, 50 to 500 stages are used, in particular 100 to 300. In the embodiment shown, 200 stages are calculated respectively for the sleep period and the power increase. This means that for the waiting period and the power increase period, the time interval for the increment of Delta T or Δt _increment between two successive calculation steps can be different, for example, the power increase period can be significantly shorter than the waiting period. For example, since the xenon concentration and/or xenon reactivity always tends to reach equilibrium during the waiting period after reaching its maximum, a fixed number of calculation steps can be used regardless of the length of the waiting period, for example 40 hours or 100 hours or more.

If the waiting period is zero, for example, when the nuclear reactor 3 is operating in the secondary mode, see below, then only the forecast for the power increase period is calculated. For calculation purposes, the prediction module 46 stores the calculated predicted xenon concentration, xenon reactivity values and/or iodine concentration values in an appropriate memory. For example, the xenon concentration value and/or xenon reactivity ρ _Xe is maintained during the sleep period (see point A in FIG. 3) and after the power up period (see point B) in FIG. 3. The increment Δt _increment in FIG. 5 corresponds to Δt _{ramp up} and Δt _{waiting period} in FIG. 1.

It should be noted that the standby prediction is only made if the nuclear reactor is to operate in tertiary control mode and not in secondary control mode (or operate in load tracking as indicated by N-SR in the drawings).

The actual iodine concentration and the actual xenon concentration or reactivity values are read respectively for the start of the waiting period for calculation if there is a waiting period, or for starting the increase in power (in the case of no waiting period or when the waiting period has expired).

It should be noted that the waiting period decreases over time, i.e. the start for the calculation is shifted each time the prediction module 46 is run again with a complete calculation of the xenon concentration, xenon reactivity and/or iodine concentration.

Based on the set value of the reactor power P _R for the waiting period and the power increase period, the xenon reactivity ρ _Xe or the xenon concentration is maintained, in particular after the waiting period (point A in Fig. 3 and 5) and after the power increase period (point B on Fig. 3 and 5).

The xenon concentration or xenon reactivity ρ _Xe after the power increase period (point B) and the xenon concentration or xenon reactivity before the power increase period or the start of the power increase (point A; either at the end of the waiting period for the tertiary control mode, or the actual xenon concentration for the secondary mode control) is used to determine by the prediction module 46 the change in xenon concentration and/or the change in xenon reactivity Δρ _Xe during the power increase period.

According to embodiments of the invention, prediction module 46 also calculates the iodine concentration for the sleep period and/or the power increase period, in particular at the end of the sleep period.

The actual value calculation module 44 and the prediction module 46 and the control module 48 together form a tandem module 50 which operates automatically and in real time in a digital reactor control system. For example, both actual value calculation module 44 and prediction module 46 respectively calculate predicted reactivity and/or xenon concentration values every 50 milliseconds. The new prediction of the prediction module 46 is based on the respectively updated actual xenon and iodine concentration values. The time to calculate the xenon reactivity for each, i.e. the standby period and the power increase period, takes about 10 seconds, respectively, based on 200 calculation steps. This means that 20 seconds is fully tertiary control and only 10 seconds is stochastic secondary control where faster computational results are desired. The accuracy of this method is discussed below.

The prediction values allow calculation of xenon reactivity support ρ _Xe during the power up phase. It should be noted that xenon reactivity and/or xenon concentration depend only on the power of the nuclear reactor and its change over time. This reactivity or xenon concentration prediction is only part of the total reactivity balance that is needed to determine the optimal position of the control rods 16 before the next power up.

The predicted change in xenon reactivity Δρ _Xe during power increase from the prediction module 46 is passed to the reactivity balance module 52, which additionally takes into account that part of the total reactivity balance that is based on the reactivity coefficients provided by the reactivity coefficient module 40. In particular, one or more of the following reactivity effects, in addition to xenon, are also taken into account to calculate the predetermined control rod position for the start of the power increase or at the start of the power increase and/or the overall reactivity balance. In particular, according to FIG. 10 visualize the reactivity balance for the reactor operator.

The (total) reactivity balance is adapted to determine, based on the reactivity values, the optimal position of the control rods 16 so that the nuclear reactor can reach a given power P _R at any time or after a waiting period using the control rods 16. This optimal position of the control rods in the present application is also can be called the preset position of the control rod to start increasing the power.

The position of the control rod can then be provided to adjust 54 the predetermined position of the control rods. In FIG. 10, the target power P _R is set at 100% of full load, which is the maximum allowable power of the nuclear reactor 3. To do this, the total reactivity (Σρ in Fig. 10) taking into account also the predicted change in xenon reactivity Δρ _Xe during power increase in the optimal case should be equal to zero.

Potential reactivity ρ _D (possible increase in reactivity due to the rise of the D-rods or control rods 16 (ΔD). The reactivity potential can be calculated based on the efficiency Γ _DM of the control rods, which is the reactivity factor provided by the reactivity factor module 40, and the actual depth of their insertion depth (ΔD) below the lower end of the L-rods, the efficiency Γ _DM is averaged over the different efficiencies depending on the depth of insertion The reactivity potential ρ _D is calculated by multiplying the efficiency Γ _DM by the actual insertion depth (ΔD) and corresponds to the reactivity potential at lift the control rods or D-rods to the lower end of the L-rods.

The control rods or D-rods must be raised to their stationary full power (nuclear reactor) position (in this case about 45 cm below the L-rods as a control margin) as shown in FIG. 10 as VFA value. This will reduce the possible increase in reactivity by the reactivity value ρ_VFA. The full power stationary position is optionally used to allow the control rods to be raised even at full power to control small fluctuations in power. Reactivity ρ_VFA control rod control margin at full load is considered separately with the reactivity factor at this depth Γ_D introductions. Reactivity potential ρ_VFA calculated by multiplying the efficiency Γ_D a predetermined full load distance to the set of L-bars, in particular to the lower end of the L-bars. Here the efficiency Γ_D, which is the reactivity factor, provides the module 40 of the reactivity factor.

Another potential reactivity value could be the reactivity ρ _L of the L rods due to the actual insertion depth of the L rods (ΔL) below their full power stationary position. The corresponding reactivity factor (Γ _L ), which corresponds to the efficiency of the L rods, is provided by the reactivity factor modulus 40 . The movement of the L-rods is mainly necessary to counteract the peak tendency of the axial power distribution at partial load. The reactivity potential ρ _L is calculated by multiplying the efficiency Γ _L by the actual insertion depth ∆L.

Another value is the reactivity ρ _P due to the future increase in reactor power to the target power P _R (ΔP) with its reactivity factor (Γ _P ) which provides the reactivity factor module 40.

The reactivity ρ _AST is due to the difference in the average coolant temperature (ACT) of the primary circuit 5 from the reference temperature at full load (ΔACT; in this example approximately 310° C. at full load) with its reactivity coefficient Γ _T , which represents the module 40 of the reactivity coefficient.

According to an embodiment, the reactivity balance may also take into account the effect of _CVCS reactivity ρ caused by the effects of BODE injection idling time by the CVCS chemical volume control system determined by the idling time simulation in combination with the corresponding boron concentration reactivity factor Γ _C . In this example, the boron concentration reactivity factor Γ _C also provides the reactivity factor modulus 40 .

In order to be able to reach the target power P _R , using in particular control rods or D-rods 16, the sum Σρ=ρ _VFA +ρ _D +ρ _L +ρ _P +ρ _ACT +ρ _Xe +ρ _CVCS of all considered reactivity values should be equal to zero. The reactivity values may even be higher or lower to calculate the sum of the reactivity, the balance of reactivity, the optimum position of the control rods and/or the preset position of the control rods to start the increase in power. At the target power P _R , i.e. after increasing the power, it should also be equal to zero. In this way, the optimum position of the control rods 16 for power increase is determined and used to calculate the reactivity balance. Thus, according to embodiments, the optimal control rod position or predetermined control rod position to start power increase is calculated based on the overall (predicted) reactivity.

If there is any deviation, for example as shown in FIG. 10 with Σρ=56 pcm, when the control rods are not in the optimum position for power increase and in particular are provided for adjusting the target position of the control rods 54, then the amount of required BODE injection is calculated based on the boron concentration reactivity coefficient Γ _C and linearized (simplified ) mixture equations (see below) in relation to the sum of the mass of the primary circuit together with CVCS to determine the amount of BODE in kg and/or kg/s (at the request of the operator). The boron concentration in the boric acid storage tanks, c _B , is required as input to the boric acid mixture equation. The mixture equations are as follows:

where Q _B is the value of the mass of injected boric acid, Q _D is the value of the mass of deionized water, c is the concentration of boric acid in the primary coolant, Δc is the change in the concentration of boric acid in the primary coolant, c _B is the concentration of boric acid in the injected boric acid, c _D is the concentration of boric acid in the injected deionized water, and M is the mass of the primary coolant along with the CVCS chemical volume control system. For example, the concentration of boric acid in the boric acid injected is about 7000 ppm (parts per million) and the concentration of boric acid in the deionized water injected is less than 1000 ppm (parts per million). For example, the mass M is about 300 tons at 310°C.

Typically, the reactance coefficients of the reactance module 40 have no time delay effects or are highly dependent on time. The reactivity coefficients in the reactivity coefficient module 40 do not include coefficients for the xenon reactivity coefficient.

In accordance with embodiments, when the nuclear reactor is operating in the tertiary control mode, based on the above considerations and factors, a time criterion is calculated, in particular using the reactivity balance module 52, which determines the time until the increase in power that is necessary to bring the control rods 16 to the predetermined position of the control rods to initiate the power increase required to increase the power target, for example by injecting boric acid or deionized water. For example, for this purpose, when calculating the time to reach the target position of the control rods to start the increase in power, not only the target position of the control rod to start the increase in power is taken into account, but also the actual position of the control rod and the primary coolant mixture based on one or more of the above equations ( 1)-(4). If the time criterion is reached, the reactivity balance module 52 is adapted to inform the float/ELPO module 56 that the float or ELPO mode, hereinafter referred to as the second and third submodes, should be terminated. The time criterion depends in part on the reactivity factors provided by the reactivity factor module 40 and/or on the actual setting of the control rods 16. Some embodiments add some extra time to have a safety margin.

Given the selected network operation modes, the following strategies and adaptations are automatically used:

If the secondary control mode is selected, for example, if button 36 is activated, which means that the waiting time should be zero (N-SR on; waiting time is zero), then the nuclear reactor should reach the target power P _R at any time, which impossible to predict. To do this, the control rods 16 must be adjusted so that the target power P _R can be achieved by moving the rod 16 at any time. This is done to predict the xenon reactivity during power up, in particular at the beginning and end of power up, to know what proportion of xenon reactivity supports power up at the selected maximum power gradient dPG/dt.

In the secondary control mode, achieving the set power is predominant compared to minimizing the addition of boric acid and/or deionized water. For example, the accumulation of xenon to the xenon maximum at partial load must be compensated by the injection of deionized water after the injection of boric acid, as shown in FIG. 6. The injection of boric acid and deionized water is carried out, in particular, automatically by the standard reactor control module 58, which holds the control rods 16 at the given points or positions provided by the control rod set point adjustment module 54, which is provided by the reactivity balance module 52. In other words, the optimal position of the control rod or the target position of the control rod to start the power increase is directly used as the set value by the control rod target position adjustment module 54 . In the secondary control mode, there is no need to calculate the xenon reactivity prediction for the waiting period. In FIG. 6 shows graphs for the secondary mode and the first sub-mode of the tertiary mode. With respect to the injection of deionized water and the position of the control rod 16, the secondary mode is shown in solid thick lines 60a, 60b. Other curves or graphs in this special case are the same for the secondary mode and the first sub-mode of the tertiary mode, discussed below. Graph 60b shows the set positions of the control rods 16 and their actual value. In FIG. 6 due to scaling, it is not possible to distinguish between the set position and the actual value of the position of the control rods or D-rods 16.

Usually, the control rods 16 (D-assembly or D-rod set) after being lowered to reduce the power of the nuclear reactor 3 are continuously gradually raised during the waiting period to the xenon maximum in accordance with the setpoint calculated by the reactivity balance module 52, because the xenon reactivity support to increase power increases due to the increased xenon burn-in effect.

According to embodiments, the tertiary control mode is detected upon the occurrence of a sleep period during which the nuclear reactor is operated at partial load, such that further minimization of BODE injection becomes possible, for example.

Depending on the waiting period, the nuclear reactor can be operated in one or more, in particular three different sub-modes. The start of the sleep period is defined as the time when the power is reduced to partial power. For example, partial power may be between 30% and 90% of the maximum power of a nuclear reactor. These three different modes are described in detail below.

When the power is reduced, the float/ELPO module 56 automatically remembers, depending on the adjusted latency, which submode is used.

According to embodiments, setpoint control during float or ELPO takes precedence over setpoint control received from reactivity balance module 52 . For example, if the float/ELPO module 56 provides information to the control rod target position adjustment module 54, regardless of whether the float or ELPO mode is used, this overrides the target positions provided by the reactivity balance module 52. In other words, depending on the adjusted latency, the float/ELPO module 56 provides information to the control rod setpoint adjustment module 54 regardless of whether the float or ELPO mode is used. The control rod set point adjustment module then ignores the set values provided by the reactivity balance module 52 .

For example, in the case of a waiting period t _PL , which corresponds to the partial load time or the duration of the partial load phase, at partial load for a time less than a predetermined time, the first submode is used. The first preset time is related to the time to reach the maximum xenon concentration. This means that only loss of xenon reactivity can be expected over this time period of approximately 8 hours. In some embodiments, the first predetermined time is, for example, 2 hours after xenon maximum or 30% of the waiting time to xenon maximum after xenon maximum. According to the embodiment shown in FIG. 6, the preset positions of the control rods 61 (thin line) are determined so that the target power P _R can be reached after the waiting time. Here, the predetermined position 61a corresponds to the predicted position of the control rods, which allows the predetermined power to be reached after the power is increased. The decrease in reactivity due to the concentration of xenon is compensated by adding deionized water via the reactor control module 58, as in the secondary control mode. The first and second lines show the phases in which boric acid and deionized water are added to the primary circuit. Compared to the secondary mode, the injection of deionized water starts a little later, as in the example of the secondary control mode above, see thin line 63a, since the control rods 16 (set of D-rods) must be removed - xenon build-up compensation - to reach their set position to increase the power, see the dotted line 63b, which reaches the set position of the control rods 61a. Boric acid injection is blocked by a xenon accumulation signal in a standard reactor control module 58 . Considering the waiting period, this predetermined position of the control rods 16 thus takes into account xenon reactivity support to increase the xenon maximum due to the increased burn-in effect from the start of the waiting period. The remaining curves of the first sub-mode of the tertiary control mode correspond to the curves of the secondary control mode in FIG. 2, i.e. when power is reduced, the actual position of the control rod corresponds to the thick line.

The amount of boric acid and deionized water is determined by the standard reactor control module 58, which holds the control rods 16 at the preset points provided by the control rod setpoint adjustment module 54, which is provided by the reactivity balance module 52. As mentioned above, the float/ELPO module 56 does not provide setpoints to the control rod setpoint adjustment module 54 . Use the given position of the control rod to start the power increase provided by the reactivity balance module 52.

The third line shows the xenon concentration over time, the fourth line shows the position of the control rods 16 (their introduction into the reactor core in centimeters), and the fifth line shows the power of the nuclear reactor 3 over time. This sub-control mode works similarly to the secondary control mode. In this case, only the waiting time is taken into account in the xenon forecast. Thus, visualization of the reactivity balance, for example, as shown in FIG. 10, in the power up phase for the reactor operator is more accurate even at the beginning of the waiting time.

In accordance with this example, a predetermined control rod position 61a for/at the end of the waiting period is shown, which is based on the total reactivity balance, including the predicted xenon reactivity, to support the increase in the power of the nuclear reactor 3 to the xenon maximum. In other words, it is the predicted predetermined position of the control rod to start the increase in power. Upon entering the partial power mode, the control rods or D-rods 16 are lowered to reduce the power of the nuclear reactor 3, in this case to about 75% of full power. As can be seen from FIG. 6, the xenon concentration increases during the waiting period. This is compensated by adding deionized water to the primary circuit 3 after reaching the predicted target position 61a of the control rods 16. At the latest before the end of the waiting period (in this case, the waiting period is about 6 hours), the control rods 16 reach the preset position 61a of the control rods in the position where the power increase starts. . During the increase in power, the xenon concentration decreases due to the effects already described above (i.e. xenon-135 burns out). After reaching the set power P _R, the xenon concentration is still decreasing, so boric acid is added to the primary circuit to reduce the reactivity, which is associated with a decrease in the xenon concentration.

In FIG. 7, the partial load waiting period t _PL is between a first predetermined time, eg 8 hours, and a second predetermined time, eg about 30 hours. This means that a gain in reactivity can be expected after xenon loss of reactivity, and this can be compensated for by moving the control rods 16 to minimize the BODE injection to the limit. To do this, use the second submode, the so-called floating mode. The second predetermined period (in this case about 30 hours) corresponds to the time when various aspects must be taken into account, in particular regarding ELPO, during long-term operation with partial load, in particular, D-assemblies or control rods must be in the "full position load" to obtain optimized fuel burnup and an optimally conditioned core in terms of interaction with the fuel pellet cladding (PCI).

In the second sub-mode, the float/ELPO module 56 informs the control rod setpoint adjustment module 54 to use the second sub-mode or float. In accordance with embodiments, module 54, upon receiving information that the second sub-mode or float mode should be used, instructs standard reactor control module 58 to disable BODE injection to compensate for changes in xenon concentration, in particular, within the upper control limit (UCL) and lower limit of regulation of the control rods 16. Thus, at a constant power of the nuclear reactor 3, the xenon concentration is compensated by moving the control rods 16 by the standard reactor control module 58, for example, indirectly by controlling the ACT. In other words, module 54 ignores the setpoints provided by reactivity balance module 52.

The second sub-mode or floating mode will be explained in detail with the help of FIG. 7. The first and second lines show the phases in which boric acid and deionized water are added to the primary circuit. The amount of boric acid and deionized water is kept to a minimum compared to previous cases because the normal control of the control rod D-assembly is deactivated with respect to BODE injection activation, and the D-assembly or control rods are moved to compensate for the change in xenon reactivity (for example, using a controller ACT in reactor control module 58). In accordance with embodiments, the control rods 16 are moved between control limits as part of standard reactor control (eg, UCL = "upper control limit" to provide a minimum distance to the lower end of the set of L-rods). Thus, it is ensured that the control rods 16 are not inserted too little. The third line shows the xenon concentration over time, the fourth line shows the position of the control rods 16 (their introduction into the reactor core in centimeters), and the fifth line shows the power of the nuclear reactor 3 over time.

In this second sub-mode, the increase in xenon concentration is compensated by the control rods 16. In other words, the control rods 16 are pulled out of the reactor core until they reach their upper control limit UCL. If additional compensation for the increase in xenon concentration is required, some deionized water is added to the primary circuit, see xenon concentration graph maximum, between approximately 6 and 8 hours. As the xenon concentration decreases past its maximum, the overall reactivity increases so that the control rods are moved down in the reactor core to a depth of about 300 cm, which they reach after about 15 hours. In this special case, the rods reach the predetermined position after about 15 hours to increase the power to the target power P _R .

If the power is to be increased to the target power P _R , in this case up to 100% of the power of the nuclear reactor 3, the control rods 16 are lifted up. In this case, the xenon concentration is reduced, so that after reaching the specified power, a further decrease in the xenon concentration is compensated by the addition of boric acid. After the minimum xenon concentration, the xenon concentration rises to an equilibrium state after about 30 hours. The creation of xenon corresponds in equilibrium to xenon burnout due to neutron absorption and xenon decay. During the rise, deionized water is again added to compensate for the change in xenon concentration.

As can be seen from FIG. 7, in which the shaded areas show a comparison with reactor control, where the control rods remain inserted for subsequent power increases. The example in FIG. 7 shows the maximum reduction in boric acid and deionized water compared to the standard regulation without waiting time. It should be noted that the decrease in the content of boric acid and deionized water increases as the end of the cycle is approached, i.e. before the fuel cells need to be replaced with new ones as additions of deionized water increase dramatically. For example, to achieve the same effect, the addition of deionized water at the end of the cycle is exponentially higher (more than 10 times higher in the last 20% of the fuel cell cycle) compared to the beginning of the cycle. Thus, the cost of cleaning or recycling the cooling water of the primary circuit 5 increases, otherwise the load flexibility will be reduced.

If the waiting time were shorter than in this example in FIG. 7 (e.g. 11 o'clock), the control rods would not have reached the set power increase control rod position or the set power increase control rod position by simply compensating for xenon depletion, with float/ELPO module 56 receiving signal from module 52 reactivity balance, for example, a "time criterion reached" termination signal to abort float. Thus, control is passed to the standard reactor control module 58, which is adapted to control the valve 28 to add additional deionized water to the primary circuit 5 so that the control rods 16 can reach the desired position of the control rods to start the increase in power, provided by the reactivity balance module 52, until the end of the waiting period for power increase. In other words, the predetermined position of the control rods to start the increase in power is provided by adjusting the predetermined position of the control rods 54 in accordance with the reactivity balance result 52 and the estimated waiting time in the xenon prediction module 46 .

If the waiting time were longer than in this example in FIG. 7 (e.g. 20 o'clock), then the control rods would exceed the preset control rod position to start the increase in power, with the preset control rod position determining the reactivity balance module 52, simply compensating for a further decrease in xenon concentration, with the float/ELPO module 56, for example, on a signal from the reactivity balance module 52, the "floating" submode is terminated, and control is transferred to the standard reactor control module 58. This is important in order to be able to subsequently introduce control rods 16 into the reactor core in the event of an emergency shutdown (provide stopping reactivity). In other words, the control rods 16 are no longer lowered because the conventional reactor control module starts boric acid injection according to a control deviation that is determined by the actual position of the control rods compared to their predicted target position provided by the control rod target position adjustment 54.

In FIG. 8, when the partial load waiting period t _PL exceeds the second predetermined time, for example, about 30 hours, the third submode is used. The third sub-mode may also be referred to as the Enhanced Low Power Operation (ELPO) mode.

This second predetermined period (in this case approximately 30 hours, but can be much longer, for example 60 hours) corresponds to the time when various aspects regarding ELPO must be taken into account: during long-term partial load operation, the D-assemblies must be in " full load position" to obtain optimized fuel burnup and an optimally conditioned core in terms of interaction with the fuel pellet cladding (PCI). For example, the second predetermined period is at least 30 hours.

The third sub-mode will be explained with the help of FIG. 8. The first and second lines show the phases in which boric acid and deionized water are added to the primary circuit. The amount of boric acid and deionized water is also kept to a minimum in this case, since the buildup of xenon (after reaching partial load) is used to bring the D-array into the "full load position". In other words, the reactor core is practically free of control rods. The third line shows the xenon concentration over time, the fourth line shows the position of the control rods 16 (their introduction into the reactor core in centimeters), and the fifth line shows the power of the nuclear reactor 3 over time.

In the third tertiary submode, the float/ELPO module 56 takes precedence over the control rod setpoint adjustment module 54 over the reactivity balance module 52's predicted setpoint. In the third sub-mode, the float/ELPO module 56 informs the control rod setpoint adjustment module 54 to use the third sub-mode or ELPO mode. In accordance with embodiments, module 54, upon receiving information that the third sub-mode or ELPO should be used, instructs that the desired position of the control rods 16 should be the "full load position" (almost free control rod or full power position). Thus, at a constant power of the nuclear reactor 3 after the control rods have reached the full load position, the xenon concentration is compensated by injection of BODE by the standard reactor control module 58, for example, indirectly through the ACT control. In other words, module 54 ignores the setpoints provided by reactivity balance module 52.

In the first step, the control rods are lowered or inserted into the reactor core to reduce the power of the nuclear reactor 3. In the example of FIG. 8 power is reduced to 75% of full power. The xenon concentration is then increased and the control rods 16 are withdrawn from the reactor core to compensate for the loss of reactivity due to the increase in xenon concentration. The control rods 16 are pulled out of the reactor core until they reach their "full load position" (almost free control rods) or are parallel to the upper control limit UCL. If further compensation for the increase in xenon concentration is required, some deionized water is added to the primary circuit, see xenon concentration graph maximum, between 6 and 8 o'clock, see ref. loop 5 of the standard reactor control module 58 introduces boric acid as determined by the set "full load position" of the control rod setpoint adjustment module 54 and the actual position of the control rods 16. According to embodiments, boric acid is added intermittently. Boric acid is added until an equilibrium of the xenon concentration is reached, i.e. when the xenon gradient is close to zero, in FIG. 8 during the period indicated by reference numeral 64.

Before the end of the waiting period, the control rods 16 must be moved to the predetermined position of the control rods to increase power. Thus, in advance of the end of the waiting period, the third sub-mode or ELPO mode is terminated in the float/ELPO sub-module 56 by receiving a "time criterion reached" completion signal from the reactivity balance module 52 . Then, the reactivity balance module 52 transmits the target positions of the control rods 16 to the control rod target adjustment module 54, which corresponds to the control rod target or pre-power-up target, and the standard reactor control module 58 injects deionized water, which moves the control rods 16 to the target position. control rods to start the power increase provided by the control rod setpoint adjustment module 54 . Deionized water is added, see reference numeral 66, to the primary circuit 5 while the control rods 16 are moving to the predetermined position of the control rods.

In this third sub-mode, the control rods are removed from the reactor core to ensure uniform burnup of the fuel rods and due to interaction with the fuel pellet cladding (PCI).

The third sub-mode or ELPO sub-mode is terminated 1 to 3 hours before the end of the timeout according to the generation of the time criterion reached signal provided by the reactivity balance module 52 based on the reactivity and balance of the primary coolant mixture. It should be noted that the control rods 16 do not go beyond the lower control limit LRL, in particular in each of the tertiary control sub-modes. The lower control limit LRL depends on the actual power P _R of the nuclear reactor. The higher the actual power, the higher the lower limit of regulation, so that at any time it was possible to stop the nuclear reactor using control rods 16.

In accordance with the embodiments, as already discussed above, the reactivity balance module 52, based on the predicted xenon reactivity and the reactivity coefficients of the reactivity coefficient module 40, further determines whether the tertiary control modes - floating or ELPO - should be terminated. To this end, the reactivity balance module 52, on the basis of the actual reactivity coefficients, the target position of the control rod, the actual position of the control rod 16 and the mixture balance (in accordance with the simplified mixture equations (1)-(4) mentioned above), determines the necessary injection time so that bring the D-assemblies into position to increase power. If this required insertion time plus tolerance becomes greater than the remaining waiting time, then the "time criterion reached" signal is activated and the ELPO mode or floating mode is terminated.

The reactor control module 58 can also operate without predicted xenon reactivity values, as well as without modules 52, 56 and 38. In this case, the predetermined position of the D-rod must be set manually.

The accuracy of a xenon predictor with 200 calculation steps for each waiting time and power up time is shown in FIG. 9 using the example of a partial load time of 15 hours. As can be seen from FIG. 9, which shows from top to bottom the xenon concentration, the prediction error, the position of the control rods or D-rods 16, and the reactor power in an example of a tertiary control mode using the second sub-mode (float), with the prediction error decreasing as the end of the sleep period approaches. This is due to the cyclically repeating calculation of the xenon reactivity prediction, which works with the remaining waiting period. Compared to the control accuracy, the error is inherently small. Even at the beginning of the waiting time, this calculation error is small and amounts to 10 pcm. This is comparable to a control rod installation deviation of approximately 8 cm if the control rod set reactance factor is 1.2 pcm/cm. Compared to the control threshold for a control rod set at partial load, the value of 30 cm is negligible.

In FIG. 10 shows a visualization for a nuclear reactor operator. Visualization can be shown on the screen. The visualization, in addition to the reactivity balance arrow discussed at the beginning, shows the remaining waiting period, as well as whether the corresponding grid is set to ELPO or floating mode. In addition, in FIG. 10 shows the target power P _R , a power increase rate of 2.1%/min (PG-Grad=dPG/dt) obtained from turbine control. "Hd. SW.Fkt." refers to the manual setting for the control rod 16 given as a suggestion to the reactor operator if the predictor influence on the reactor control should be disabled, while "Hd.SW.Fkt. actual value" is the actual effective value when the reactor is controlled by control rods 16.

In accordance with some embodiments, the time constants and control intensity ranges may be adapted to control the nuclear reactor in the case of the selected primary control mode.

According to embodiments, the method or algorithms for predicting xenon minimize calculation steps and are adapted to the selected power grid control mode to determine the contribution of xenon to the expected phase of power increase, which is necessary for real-time digital reactor control implementation. The method used in the embodiments allows all power grid related control modes (even unexpected transients such as load deviation from internal load), including stochastic remotely controlled load changes using xenon tandem calculation with one xenon actual value calculation and iodine as the basis for the second predictive calculation of the xenon contribution to the power increase phase.

In some embodiments, any feature of any embodiment described herein may be used in conjunction with any feature of any other embodiment described herein.

Claims (40)

1. A method for controlling a nuclear power plant containing a nuclear reactor (3) with pressurized water, having a reactor core that generates energy, a primary circuit (5) connecting the reactor core to a steam generator (9), one or more control rods (16) , which are able to move into the reactor core to control the power of the reactor core, an injector device (22, 23, 24, 26, 28, 30) for injecting boric acid and / or deionized water into the primary circuit (5) to control the reactivity of the core reactor, including determination of the actual power (P _R ) of the nuclear reactor (3), automatic determination of the actual xenon concentration, the actual iodine concentration and/or the actual xenon reactivity, obtaining the target power and the power gradient (dPG/dt) for the period of power up to the target power, characterized in that a waiting period and/or a remaining waiting period are obtained during which the nuclear reactor (3) operates at partial power until it increases the power to a target power exceeding the specified partial power, for the end of said waiting period and/or the remaining waiting period, xenon reactivity and/or xenon concentration are calculated based on the actual xenon concentration, the actual iodine concentration and the obtained waiting period, xenon reactivity and/or xenon concentration are calculated for the end of the power increase period, calculate the predetermined position of the control rods at the beginning of the power increase for said one or more control rods (16) based on the calculated xenon reactivity and/or xenon concentration at the end of the waiting period and at the end of the power increase period so that the specified power increase can be performed with using control rods (16), during the waiting period, said one or more control rods (16) are positioned based on the waiting period and the specified position of the control rods at the beginning of the increase in power so that at the end of the specified waiting period, the specified one or more control rods reach the specified position of the control rods at the beginning of the increase power, moreover, if the waiting period exceeds the first predetermined time, allowing to raise the xenon concentration to the maximum value, then said one or more control rods (16) are moved from the reactor core to compensate for the loss of reactivity due to the increase in xenon concentration, and before the end of the specified waiting period, said one or more control rods (16) are moved into the reactor core to the specified predetermined position of the control rods at the beginning of the increase in power. 2. The method according to claim 1, in which the calculation of the given position of the control rods at the beginning of the increase in power is also based on one or more reactivity values and / or reactivity factors of the nuclear reactor, in particular on one or more reactivity coefficients of said one or more control rods, the reactivity coefficient of one or more L-rods, the change in reactivity due to the average coolant temperature difference (ACT) between the actual power and the target power, the change in reactivity due to the difference between the actual power (P _R ) and the target power, and/or the contribution to the reactivity subsequent flow of injected boric acid or deionized water combined with the boric acid ratio in the primary coolant. 3. The method according to claim 1 or 2, wherein the calculation of the target position of the control rods at the beginning of the increase in power is also based on the preset position of the control rods (16) at full power and/or the preset position of the L-rods at full power. 4. The method according to any one of the preceding claims, wherein if the control rods (16) reach the upper control limit or full load position when withdrawing from the reactor core, then deionized water is added to maintain the reactor (3) at partial power to compensate for the loss of reactivity from -for increasing the concentration of xenon, in particular, to ensure controllability of the reactor power. 5. The method according to any of the previous paragraphs, in which also determining a time limit for moving said one or more control rods (16) to a predetermined position of the control rods at the beginning of the increase in power based on the actual position of the control rods, the predetermined position of the control rods at the beginning of the increase in power and the actual concentration of boric acid in the primary coolant, in order to move said one or more control rods (16) into the reactor core to a predetermined position of the control rods at the beginning of the increase in power, up to a certain time limit, by injecting deionized water into the primary circuit, and add deionized water to the primary circuit (5). 6. The method of claim 5, wherein the time limit is also determined based on the minimum deionized water feed rate. 7. The method according to any one of the preceding claims, wherein when the waiting period is shorter than a second predetermined time which is longer than the first predetermined time, said one or more control rods (16) are moved to the reactor core after the xenon concentration has reached its maximum during the specified waiting period in order to compensate for the increase in reactivity due to the decrease in xenon concentration. 8. The method according to any one of paragraphs. 1, 4, 7, in which when the waiting period is shorter than the second predetermined time, which is greater than the first predetermined time, then if, during the movement into the reactor core, the control rods (16) reach the specified predetermined position of the control rods at the beginning of the increase in power, then boric acid is added to the primary circuit and the control rods (16) are maintained in the indicated predetermined position of the control rods at the beginning of the increase in power, in particular to ensure the residual reactivity of the shutdown reactor. 9. The method according to any one of the preceding claims, wherein when the waiting period exceeds a second predetermined time which is longer than the first predetermined time, after reaching the maximum xenon concentration during said waiting period, boric acid is added to the primary circuit (5) to compensate for the increase reactivity due to a decrease in the xenon concentration, while, in particular, until the end of the waiting period, the control rods are left in the position of the upper limit of control or full power until they move into the reactor core to the specified predetermined position of the control rods at the beginning of the increase in power. 10. The method according to any one of the preceding claims, wherein the first predetermined time corresponds to the time 2 hours after the xenon maximum or the time after the xenon maximum corresponds to 30% of the waiting time to the xenon maximum. 11. A method according to any one of the preceding claims, wherein the first predetermined time is from 6 to 10 hours and/or the second predetermined time is from 20 to 60 hours. 12. The method according to any one of the preceding claims, wherein in order to calculate the target position of the control rods at the beginning of the increase in power, the total reactivity is calculated, including the xenon reactivity at the end of the standby period and at the end of the increase in power period when the power is increased to the target power. 13. Controller for a nuclear power plant containing a nuclear reactor (3) with pressurized water, having a reactor core that generates energy, a primary circuit (5) connecting the reactor core to a steam generator (9), one or more control rods (16) , capable of moving into the reactor core to control the power of the reactor core, an injector device (22, 23, 24, 26, 28, 30) for injecting boric acid and / or deionized water into the primary circuit (5) to control the reactivity of the reactor core , characterized in that it is made with the possibility determine the actual power (P _R ) of the nuclear reactor (3), automatically determine the actual xenon concentration, the actual iodine concentration and/or the actual xenon reactivity, obtaining the target power and the power gradient (dPG/dt) for the power increase period until the target power is reached, characterized in that the controller is configured to also: obtaining a waiting period and/or a remaining waiting period during which the nuclear reactor (3) operates at partial power until it increases the power to a target power exceeding the specified partial power, calculation of the xenon reactivity and/or xenon concentration at the end of the waiting period and/or the remaining waiting period based on the actual xenon concentration, the actual iodine concentration and the received waiting period, calculation of xenon reactivity and/or xenon concentration at the end of the power increase period, calculating a predetermined position of the control rods at the beginning of the power increase for said one or more control rods (16) based on the calculated xenon reactivity and/or xenon concentration at the end of the waiting period and at the end of the power increase period so that the power increase can be performed using control rods (16), positioning during the waiting period of said one or more control rods (16) based on the waiting period and the set position of the control rods at the beginning of the increase in power so that at the end of the waiting period, the specified one or more control rods reach the specified set position of the control rods at the start of the increase power, moreover, if the waiting period exceeds the first predetermined time, allowing to raise the xenon concentration to the maximum value, then the controller is configured to also move said one or more control rods (16) out of the reactor core to compensate for the loss of reactivity due to the increase in xenon concentration and before the end of the specified waiting period, move the specified one or more control rods (16) into the reactor core to the specified predetermined position of the control rods at the beginning of the increase in power. 14. The controller for a nuclear power plant according to claim 13, which is configured to perform the method according to any one of paragraphs. 1-12.

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